1. Field of the Invention
This invention relates to a Duct Access Door for sealingly closing a circular access hole formed in an air duct so that access to the interior of the duct can be gained as desired.
2. Description of the Prior Art
In modern heating, ventilating and air conditioning (HVAC) systems, sheet metal duct work is utilized to convey conditioned air throughout buildings. Conventionally, access holes are formed in the duct work at various locations for various purposes. The access holes may provide access to clean the interior of the duct work or to inspect turning vanes, fire dampers or other hardware inside the duct. Existing clamping type access doors are rectangular or oval in shape. Prior to this invention round holes were closed with simple patches that do not allow easy access later or more complicated doors which are more expensive.
Duct access doors in the prior art have been formed from sheet metal having an outer panel and an inner panel that are connected by bolts or other means of biasing them toward each other. A gasket is provided around the periphery of the access door. Because of the rectangular or oval shape of the prior art duct access parts, the inner panel of the door may be inserted into the duct while the outer panel of the door remains outside the duct. The two panels are then tightened together to clamp the duct wall between them so that the gasket engages the duct wall and one of the panels to seal the duct access port.